The present invention relates to a novel herbicidal composition in the form of solid water dispersible granules (WDG) containing the compound N-phosphonomethylglycine (glyphosate acid) in an admixture with a particular non-ionic surfactant. This composition provides a combination of manufacturing and weed killing (i.e., herbicidal) advantages that heretofore have been unattainable with the use of either glyphosate acid or glyphosate in salt form. The present invention also relates to a novel process for preparing this novel WDG composition.
Glyphosate in the form of its salts, as opposed to glyphosate in its acid form, is the most common form of glyphosate that is used as an active agent in agriculture and industrial herbicidal liquid formulations (soluble liquids) or solid formulations (soluble powders or water dispersible). Glyphosate acid has the following structure: ##STR1## Glyphosate salts have been preferred because of glyphosate acid's relative lack of solubility in water and other solvents that are commonly used both to process glyphosate and to apply glyphosate in herbicidal applications. Thus, glyphosate salts have been chosen as the form to use in the vast majority of herbicidal applications because, before this invention, they were easier to use both when manufacturing the herbicidal formulations and when the end user makes the final herbicidal formulation that was applied to weeds and other undesired plants.
The glyphosate salt compositions are generally used in liquid formulations composed of glyphosate itself in the amount of from 2% to 40% by weight in a salt form and a suitable coadjuvant (i.e., surfactant) which enhances the absorption of the active agent in the undesired plants. The salt forms commonly contain glyphosate with amines or other cations. The amines and cations include isopropylamine in the case of liquid formulations (soluble liquids) and ammonium or sodium salts for solid type formulations such as WDG. The past work of others has largely focused on solving problems associated with making the glyphosate salt compounds easier to process and then apply as herbicides. These problems with using glyphosate salts include their hygroscopic nature which can lead to processing (e.g., clogging) and storage (e.g., deliquescence) problems.
The reported attempts to use glyphosate acid instead of the salt forms of glyphosate to avoid the aforementioned problems associated with using the salt forms have not been capable of producing a composition with the advantages of the present invention. These reported compositions have substantial disadvantages which include disadvantages in the manufacturing of the herbicidal composition, requiring the use of unfavorable processing conditions, or the addition of extra ingredients such as acid acceptors and extrusion aids. Other disadvantages arise in the final use of the composition to kill undesired plants.
Specifically, U.S. Pat. No. 5,118,338 described a water soluble herbicidal formulation in the form of powder or granules which can include glyphosate acid and a non-ionic surfactant. This surfactant consists of a polyglycolether of a fatty alcohol having from 16 to 18 carbon atoms which is ethoxlyated with about 25 units of ethylene oxide per mole of fatty alcohol. The surfactant that was chosen is itself in a granular or powdery form and the disclosure explicitly excludes the use of waxy surfactants. This formulation does not allow the preparation of granules by direct extrusion in the absence of further extrusion aids.
EP-A-0 582 561 describes a herbicidal formulation containing glyphosate in admixture with a surfactant which is preferably liquid at ambient temperature with an extrusion aid added consisting of a polyalkyleneglycol. All of the formulations which are specifically disclosed in the working examples relate to glyphosate in a salt form with an alkali metal or ammonium. The use of an extrusion aid is described as essential in order to obtain anhydrous formulations in granular form by the extrusion process.
WO 92/12637 describes anhydrous formulations of glyphosate containing an acid acceptor and optionally a surfactant. Thus, this formulation requires the addition of an extra ingredient, the acid acceptor, in order to make the composition processable and useable as a herbicide.
In light of these problems, it would be desirable to provide herbicidal compositions and formulations containing glyphosate acid that do not have the substantial disadvantages of the compositions and formulations of the past.